Heat-resisting alloys containing cobalt



Patented Mar. 19, 1946 OFFICE HEAT-BESISTING ALLOYS CONTAINING COBALT Gunther Mohling, Loudonville, N. Y., assignor to Allegheny Ludluln Steel Corporation, a corporation of Pennsylvania '13Cialms.

Drawing. Application April 21, 1944.

Serial No. 532,209

In myapplication for patent Serial No. 473,387,

illed 23, 1043, I have set forth the dis- 4 covery that ferrous alloys containing relatively large amounts of chromium and nickel and sub stantial but smaller amounts of molybdenum, tungsten and columbium in a balanced ratio, not

only have superior strength at high temperatures than other heat resisting alloys of comparable cost, but'also are characterized by structural stability and by the fact that they are more readily workable under ordinary commercial practices than known alloys having comparable heat resisting characteristics and containing substantial amounts of chromium.

My present invention also relates to alloys capable of being eifectivly employed at'high temperatures and even under conditions where they are subjected to heavy stresses while existing at such temperatures. object of my present invention is to produce alloys which may be readily fabricated into structural parts or articles and which are capable of being effectively employed as the working parts of such mechanisms as gas turbines.

A further object of my invention is to produce a heat resisting alloy which has structural stability at temperatures ranging from about 1000 F. to approximately 1600 F.

I have discovered that cobalt additionsto heat resisting alloys containing substantial amounts of chromium have a beneficial influence on the strength atheat of such alloys, provided the other alloying constituents are properly balanced. I have also discovered that additions of substantial amounts of cobalt to such balanced alloys have a beneficial effect in alloys containing chromium within the range of from about 12% to 22% and nickel'within the range of from about 18% to 31 That is to say, my present invention involves the production of an alloy having highly desirable characteristics under heat and containing cobalt within the range of from about 9% toabout 50%, chromium within the range of from about 12% to about 22% and nickel within the range of from about 18% to about 31%.

' In Table I, I have set forth two types of alloys embodying my invention, one containing chmmium within the lower portion of the above range and, the other containing chromium within the upper portion of that range and with each including suflicient nickel to render the alloyaustenitic. For comparison purposes the following table also sets forth an alloy designated as S495 and S588 which are similar to the alloys constituting embodiments of my present invention, except that they do not include cobalt as an alloying constituent.

That is to say, an

Tim: I y rms-m Type 8-588 Melt 1 Remainder substantially all iron except for usual impurities in commonamounts.

It should be stated that the melts or alloys set forth by the above table are merely exemplary of many such melts that have been made and which that nickel should be present in an amount sums cient to insure a stable austenitic character under all conditions of service.

These melts were forged, rolled and machined into conventional test pieces. They were tested under a variety of constant loads while existing at temperatures within the range of from about 1000 F. to about 1600 F. for the purpose of ascertaining the strength" and creep characteristics of the various alloys under various load and temperature conditions. The results of these tests,

eeesssssa Hrs. to rupture Elongation. per cent when compared with the results of similar tests involving substantially similar alloys (S495 and 8588) except for the absence of cobalt, disclosed that in almost every instance the life of the alloy at a given load and at a given temperature is considerably increased by the cobalt addition.

Table II shows the results of rupture tests on 8495 type of alloys with and without cobalt and with cobalt varying within the range of from about 10% to about 30% and in each case replacing a corresponding amount of iron. The tests were run at the temperature noted-viz.. 1200" F., 1300 F., 1500* F. and 1600 F.- -the time required to rupture is given in hours, the percentage of reduction is set forth, the load is set forth in pounds per square inch and thehardness of (a) Test temperature-1200 F. State or test pieces: 1 hr. at 2250 F'., water quench, aged 16 hrs. at 1400 F. air cooled.

Melt

Cobalt content None (I) LOAD, 40,000 P. S. 1.

Reduction do. Hardness, Brinell (2 LOAD, 50,000 P. s. 1'.

Hrs. to rupture Elongation. "per cent. Reduction.-. ..do Hardness, Bnnell Melt LOAD, 30,000 P. S. I.

(a) Test temperature-160T F. State of test pieces: 1 hr. at 2250-F., water quench, aged 16 hrs. at 1600: F. air cooled.

Melt

LOAD, 10,000 I. S. I.

Melt

Cobalt content ..per cent.. None 10 19.02 30 (1) LOAD, 20,000 P. S. I.

Hrs. to rupture 78 87 72 170 Elongstion--- r cent 7 7 22 5 Reduction do.' 23 15 30 9 Hardness, Brinell 255 255 229 248 (2) LOAD, 17,500 P. S. I

Hrs. to rupture 285 272 443 Elongation.--- .per cent" 8 24 7 Reduction -do 24 32 18 Hardness, Brinel 241 229 248 From the foregoing table, it is apparent that the alloy S497, containing about 20% cobalt, is considerably stronger than S495 (with no cobalt) at 1200 F., 1300 F. and 1600 F. (see Table II, a, b and c) At 1500 F. about 30% cobalt is required to bring about a similar increase in life, while at that temperature alloys containing 10% and 20% cobalt show strength characteristics about equal to those of S495. The explanation for this is that 1500 F. is about in the middle of the precipitation hardening range and a major portionof the strength of the alloy at that heat is due to this fact. That is to say, the precipitation hardening is more effective than 10% or 20% cobalt additions at 1500 F.

Table III sets forth results of similar tests on type S588 alloys and as in Table II, the cobalt content of the alloy tested is specifically noted.

TABLE III Rupture test of S588 type alloys at temperatures noted (a) Test temperature1350 F. State of test pieces: 1 hr. at 2300" F., water quench, aged 16 hrs, at 1400 F. air cooled 4 (S816 at 2350 F., etc.)

Melt sass e752 ssso sis? S816 Cobalt content per cent" None 10 19. 35 30 43.

(1) LOAD, 35,000 P. S. I.

Hrs. to rupture s 3'1 35 as 373 Elongationnnper cent- 15 14 24 12 8 Reduction -do. 15 18 24 17 0 Hardness, Brinell- 262 241 255 241 321 (2) LOAD, 30,000 P S. I.

Hrs. to rupture 39 142 131 Elongation.. -per cent.. 11 10 I 19 Reduction do.--- 16 14 24 Hardness, Brinell 285 $35 277 (3) LOAD, 30,000 P. S. 1. STATE: AS CAST Hrs. to rupture... 273 Elongation per cent.-- 6 action do.... 5 Hardness, Brine ll 28.

' (0) Test temperature-1500' r.

State ottest pieces: 1 hr. at 2300" F., water quench, aged 16 hrs. at 1500 F., air cooled ($816 at 2350" F., etc.)

Melt

S588 S762 S590 S787 5816 Cobalt content per cent None 10 19. 35 30 43. 70

(1) LOAD, 20,000 P. S. 1.

Hrs. to rupture t 53 73 114 191 447 Elongation .per cent 6 7 12 18 1 11 Reduction .do.. 10 13 23 29 9 Hardness, Brinell 269 285 293 302 311 (2) LOAD, 20,000 P. S. I. STATE: AS CAST Hrs. to rupture 38 77 Elongation per cent 8 4 Reduction do 18 Hardness, Brinell 255 255 (c) Test temperature-1600 F.

State of test pieces: 1 hr. at- 2300" F., water quench, aged 16 hrs. at 1600 R, air cooled ($816 at 2350 F., etc.)

From the foregoing table it is apparent that cobalt additions to the ferrous alloy S588 from to oxidation or corrosion is more important than high strength at heat.

Table III also indicated that the heat treatment favorsalloys containing no cobalt and also alloys of the lower, cobalt content whether or not those alloys contain the larger or smaller amounts of chromium. As to the heat treatment, it should be noted that after the alloy is cast and partially fabricated by forging and/or rolling to the desired size and shape, the pieces so fabricated were then given a short time heat treat at a high temperature, 1. e., within the range of from-about 2150 F. to about 2400" F. for approximately an hour. They were then rapidly cooled, preferably by a water quench, and then subjected to an aging treatment at a temperature within the range of from about 1300 F. to about 1600 F. for

Q about sixteen hours and then air cooled, all as about 10% to about 45% have a progressive effect in strengthening the alloy at 1350 F., 1500 F. and 1600 F. While the increase in strength is not strictly proportional to increases in the amount of cobalt the strength does, however, increase with increases, in the cobalt content. As indicated by Table III, some compositions; constituting embodiments of my invention, disclose excellent strength at heat in the cast form. For this reason final products, such for example as blades for gas turbines, may be made by a precision Or lost wax casting process. As to this, it might also be notedthat in som applications, where the alloy is to be used in the cast state, substantially larger amounts of one or more ,of the carbide forming elements (Mo, W and Cb) may be advantageously used. That is to say,

say, the chromium range may be extended-to about 35.00% in cast structures where resistance more fully set forth in my application, Serial No. 515,924 filed December 28, 1943. It should also be noted that the tests run on alloy S816 and, set forth by Table III, were run after test pieces formed from that alloy had been subjected to a short time heat treatment at 2350 F. followed by a water quench and an aging treatment as described. I

For the purpose of summing up, I note that my present invention comprises heat resisting alloys containing cobalt and including the elements below set forth within the ranges noted:

Carbon about 0.10% to about 0.70% Chromium about 12.00% to about 22.00% Nickel about 10.00% to about 31.00% Molybdenum about 2.00% to about 6.00%

Tungsten about 2.00% to about 6.00%

Columbium about 2.00% to about 6.00% Cobalt about 9.00% to about 50.00%

with or without usual commercial amounts of such alloying elements as silicon and manganese and with the remainder iron plus usual contaminating substances in common amounts.

In the process of proving my invention, I have made several hundred melts and have forged, rolled andtested the same for the purpose of establishing their heat resisting characteristics and strength at temperatures between 1100 F. and 1800" F. The data so obtained causes me to define my invention, as above set forth and to state that all alloys including the alloying constituents above set forth within the ranges noted, will disclose superior characteristics such as are herein commented upon.

While I have set forth examples of alloys embodying my invention, it will be apparent that various changes in the alloying constituents may be made so long as such changes do not alter the basic nature of the alloy for the purpose of my invention nor destroy the balance which is essential to render the cobalt addition highly effective as an alloying constituent. It will be apparent, for example, that alloying constituents such as manganese and silicon may be increased above or reduced below the ranges previously indicated, that eneor more of the elements, molybdenum. tungsten and columbium may be used in amounts lower than the ranges above set forth and that some additional alloying element may be added without changing the essential character' of the alloy. For these reasons the term balance substantially iron, as employed in the appended claims, contemplates that the balance of the composition is largely iron but may contain percentages of additional non-ferrous alloying elements of such nature and in such quantity as not to alter the basic nature or the alloy, nor destroy the balances here contemplated.

What I claim is:

1. A heat resisting alloy containing carbon within the range 01' from about 0.10% to about 0.70%, chromium from about 12.00% to about 20.00%, nickel from about 10.00% to about 30.00%, cobalt from about 9.00% to about 50.00%, molybdenum, tungsten and columbium each within the range of from about 2.00% to about 6.00% and the balance substantially iron.

2. A heat resisting alloy containing carbon within the rangeoi from about 0.10% to about 0.70%, chromium within the range or from about 12.00% to about 22.00%, nickel in amounts at least equal to the chromium content, molybdenum, tungsten and columblum, ea'ch within the range of from about2.00% to about 6.00%, cobalt within the range of from about 9.00% to about 50.00% and the balance substantially iron.

3. A heat resisting alloy containing from about 0.10% to about 0.70% carbon, chromium from about 12.00% to about 22.00%, nickel in amounts at least equal to the chromium, substantially equal amounts of 'molybedenum, tungsten and columbium each within the range of from about 2.00% to about 6.00%, cobalt from about 9.00%

to about 50.00% and the balance substantially at least substantially equal to the chromium content, molybdenum, tungsten and columblum in substantially equal amounts, each approximately 4.00%, cobalt from about 9.00% to about 50.00% and the balance substantially iron.

6. A hot worked and annealed article made from. an alloy consisting of carbon from about 0.10% to about 0.70%, chromium from about 12.00% to about 22.00%, nickel in an amount at least substantially equal to the chromium content,, molybdenum, tungsten and columbium, each within the range of from about 2.00% to about 6.00%, cobalt from about 9.00% to about 50.00% and the balance substantially iron.

7. A but worked, high-te'mperature-annealed and age-annealed article made from an alloy consisting of carbon within the range 01' from about 0.20% to about 0.60%, approximately 14.00%

chromium, approidmately 20.00% nickel, molybdenum, tungsten and columbium, each approxi- 8. A hot worked, high-temperature heattreated and aged article formed from an alloy consisting of carbon of about 0.10% to about 0.70%, approximately 20.00% chromium, nickel in an amount at least substantially equal to the chromium, molybdenum, tungsten and columbium, each from about 3.50% to about 4.50%, cobalt from about 9.00% to about 50.00%, manganese and silicon each from about 0.50% to about 2.00% and the balance substantially iron.

9. A heat resisting alloy consisting of carbon within the range of from about 0.10% to about 0.70%, chromium within the range of from about 12.00% to about 22.00%, nickel in an amount sufflcient to produce a stable austenitic alloy under conditions of use, molybdenum, tungsten and columbium each withinthe range of from about 1.00% to about 6.00%, cobalt within the range of from about 9.00% to about 50.00% and the balance substantially iron.

10. A high-temperature annealed and aged article made from an alloy consisting of carbon within the range of from about 0.10% to about 0.70%, chromium within the range of from about 12.00% to about 22.00%, nickel in an amount sufficient to produce a stable austenitlc under all conditions of use, molybdenum, tungsten and columbium each within the range of from about 1.00% to about 6.00%, cobalt within the range of from about 9.00% to about 50.00% and the balance substantially iron.

11. A heat resisting alloy consisting of carbon within the range of from. about 0.10% to about 0.70%. chromium within the range of from about 12.00% to about 35.00%, nickel in an amount suificient to insure a stable austenitic alloy under conditions of use, cobalt within the range of from about 9.00% to about 50.00%, molybdenum, tungsten and columbium, each within the range of from about 1.00% to about 10.00% and the balance substantially iron.

12. A heat resistant cast article made from an alloy consisting of carbon within the range of from about 0.10% to about 0.70%, chromium within the range of from about 12.00% to about 35.00%, nickel in an amount at least sufficient to insure a stable austenitic alloy under all conditions 01' use, cobalt from about 9.00% to about 50.00%, molybdenum, tungsten and columbium.

each within the range of. from about 1.00% to about 10.00% and the balance substantially iron.

13. A heat resisting alloy containing carbon within the range or from 0.10% to 0.35%, chromium from 15.0% to 20.0%, nickel from 15.0%

to 25.0%, cobalt from 10.0% to 25.0%, molyb-.

denum from 2.0% to 3.5%, tungsten from 2.0%

to 6.0%, columbium about 2.0% and the balance substantially iron. I

GUNTHER MOI-ILING. 

